To flash ROCK960 board, you need to install the rkdeveloptool, which is an open source cross platform command line tool. To build rkdeveloptool, you should have installed brew on your macOS.
Install build tools:
brew install automake autoconf libusb
Clone the source code and build:
git clone https://github.com/rockchip-linux/rkdeveloptool
cd rkdeveloptool
autoreconf -i
./configure
make
Now you have rkdeveloptool executable at the current directory.